Free radical-induced oxidative stress is a major factor in the long-term tissue degradation associated with aging. Living cells during their normal functions continuously produce free radicals. Free radicals are highly reactive substances capable of reacting irreversibly with many biological molecules, thus causing progressive deterioration of the biological system that eventually results in aging and death. Free radicals are normally neutralized by the body's production of antioxidant enzymes and nutrient-derived antioxidants. Numerous studies have been conducted to determine whether antioxidants can reduce oxidative stress or affect the longevity of animals. While animals currently live longer and have a better quality of life due to improved nutrition and medical care, there is still a need for new or alternative methods and compositions for increasing the longevity of animals, in particular animals that are already old.